Diet-induced nephrocalcinosis and urinary excretion of albumin in female rats

This study was carried out to test the hypothesis that diet-induced nephrocalcinosis causes enhanced loss of albumin in urine, irrespective of the composition of the nephrocalcinogenic diet. Female rats were fed various purified diets for 28 days. There was a control diet (0.5% Ca, 0.04% Mg, 0.4% P, 15.1% protein, wt/wt), a low Mg (0.01% Mg), a high protein (30.2% protein) and a high P diet (0.6% P). The low Mg and high P diet induced nephrocalcinosis as demonstrated histologically and by markedly increased concentrations of kidney Ca. In rats fed the high protein diet, nephrocalcinosis was essentially absent. Group mean values of urinary excretion of albumin and plasma concentrations of urea were increased in rats fed either the low Mg or high P diet. The high protein diet did not affect urinary albumin but caused lysozymuria which was not seen in the other groups. Plasma urea was increased in rats fed the high protein diet. In individual rats, the concentration of Ca in kidney and urinary albumin excretion were positively correlated. It is suggested that nephrocalcinosis in female rats induced by either low Mg or high P intake causes kidney damage which in turn leads to increased concentrations of albumin in urine and urea in plasma.     

Commercial rodent diets and nephrocalcinosis in weanling female rats.

This study addresses the questions to what extent commercial rodent diets would induce nephrocalcinosis, and which dietary components would be responsible for inducing this condition. For this purpose, 10 commercial diets were analysed for selected components and fed to weanling female rats. On the basis of histological inspection of kidney sections, two diets were found to produce significant nephrocalcinosis. The condition could be considered relatively mild because concentrations of Ca in kidney tissue were not increased. There was considerable variation between the commercial diets in the (analysed) concentrations of Ca, P, Mg and protein as well as in the diet-induced urinary pH, urinary volume and caecal weight. Of these parameters, only the dietary Ca:P ratio and group mean urinary pH correlated significantly with the observed variation in group mean calcification scores, the relationships being negative. It is suggested that the Ca:P ratio of commercial rodent diets is an important determinant of nephrocalcinosis.     

Dietary supplementation with Pluronic L-81 modifies hepatic secretion of very low density lipoproteins in the rat

Supplementation of high fat/cholesterol-enriched diets with polyoxypropylene-polyoxyethylene copolymers containing 90% hydrophobic constituents has been found to impair enteric secretion of chylomicrons, lower plasma levels of very low density (VLDL) and low density (LDL) lipoprotein cholesterol and prevent diet-induced hypercholesterolemia and atherosclerosis. These agents are known to be absorbed from the gastrointestinal tract and excreted in bile. In order to determine whether dietary supplementation with this group of hydrophobic poloxalenes influences hepatic secretion of triglyceride-rich lipoproteins, groups of rats were maintained for 21-34 days on either standard chow, semisynthetic diet containing 10.0% safflower oil/1.0% cholesterol, or each of the above diets supplemented with the hydrophobic poloxalene Pluronic L-81. At the end of the feeding period, newly secreted hepatic VLDL were isolated from 2-hr recirculating liver perfusates, quantitated, and characterized. Compared to perfusions in chow-fed rats, perfusion experiments in rats fed the high fat/cholesterol-enriched semisynthetic diet revealed a 3.1-fold increased net hepatic VLDL secretion rate; enrichment of secretory VLDL in cholesteryl esters and in C18:2 core lipid fatty acids; and a shift in the size distribution of secretory VLDL towards larger particles. When the 0.5% Pluronic L-81 was included in the high fat/cholesterol-enriched semisynthetic diet, the net hepatic VLDL secretion rate fell significantly and the physicochemical properties of secretory VLDL in these rats were found to resemble those of chow-fed animals. Supplementation of the chow diet with L-81 resulted in a significant fall in the net hepatic VLDL secretion rate from that observed in rats fed chow alone. Compared to rats fed chow alone, perfusate VLDL from rats fed each of the other experimental diets contained markedly lower amounts of both apoB molecular weight variants, as analyzed by gradient gel electrophoresis and densitometric gel scanning. Since previous studies have demonstrated that VLDL are the major cholesterol transport lipoproteins following fat/cholesterol feeding; a precursor-product relationship exists between fat/cholesterol-induced hepatic VLDL and plasma VLDL; such particles are capable of delivering cholesterol to the arterial wall; and dietary supplementation with hydrophobic poloxalenes prevents both the increase in plasma VLDL-cholesterol and diet-induced atherosclerosis, it is possible that dietary supplementation with hydrophobic poloxalenes may influence the atherogenic process through direct and/or indirect effects on hepatic VLDL transport.     

Vitamin D, within its range of fluctuation in commercial rat diets, does not influence nephrocalcinogenesis in female rats.

Massive, toxic doses of vitamin D have been shown to cause nephrocalcinosis in rats, but the effect of this vitamin within its range of fluctuation in commercial rat diets was unknown. Therefore, in two experiments with young female rats, the effect on nephrocalcinosis of a moderately increased level of vitamin D in the diet was studied, that is 5000 IU/kg versus the recommended concentration of 1000 IU/kg. This was done using purified diets with 0.5% (w/w) calcium and 0.04% magnesium containing either 0.2 or 0.6% phosphorus (P). Rats fed the diets containing 0.6% P showed severe kidney calcification compared to those fed the 0.2%-P diets. The level of vitamin D in the 0.2 and 0.6%-P diets did not affect kidney calcification. Bone density was increased after feeding diets containing 5000 instead of 1000 IU of vitamin D/kg. This study suggests that, within 28 days, a moderate increase of the amount of vitamin D in the diet has no influence on the development of kidney calcification. This in turn suggests that the variation in nephrocalcinosis severity and incidence seen in practice in rats fed different commercial diets is unlikely to be related to the different vitamin D concentrations in these diets. However, in rats fed such diets bone metabolism may be influenced differently.     

Phosphorus-induced nephrocalcinosis in female rats: a study on regression and clinical abnormalities

The question addressed was whether preestablished phosphorus (P)-induced nephrocalcinosis would regress after dietary P restriction. Female rats were fed purified diets containing either 0.2% (w/w) P (low P) or 0.6% P (high P). After 29 days, the high-P diet had caused massive nephrocalcinosis as demonstrated chemically (by the analysis of calcium in kidney) and histologically (by inspection of kidney sections stained for calcium phosphate deposits). Switching rats from the high P to the low P diet did not result in a decrease in the degree of nephrocalcinosis within 91 days. Thus, P-induced nephrocalcinosis may not regress upon subsequent P restriction. Rats that had been fed either the 0.2 or 0.6% P diet for 56 days were examined clinically with respect to 14 selected variables. None of the variables discriminated between rats with or without nephrocalcinosis. This might imply that P-induced nephrocalcinosis in female rats does not cause significant discomfort.     

Influence of diet on the development of nephrocalcinosis in the rat

A histological examination of the effect of a purified diet containing 20% alpha protein (an alkali-treated soyprotein) on the development of nephrocalcinosis induced by intraperitoneal injections of 0.5 neutral (pH 7.4) sodium phosphate was carried out in female weanling rats. Animals that were fed a standard commercial laboratory diet and given daily injections of phosphate for six or ten days developed a form of nephrocalcinosis that consisted mainly of intraluminal (intratubular) calcification at the junction of the outer and inner stripes of the outer medulla and in the inner stripe of the outer medulla. By contrast, rats that were fed the alpha protein diet and given injections of phosphate for six or ten days developed a form of nephrocalcinosis that was characterized primarily by a type of tubular basement membrane calcification at the junction of the inner stripe of the outer medulla and the inner medulla. The differences in nephrocalcinosis between the two dietary groups and the fact that an alpha protein diet by itself can cause renal calcification, leads to the suggestion that some component(s) or factor(s) in the alpha protein diet strongly influence(s) the development of nephrocalcinosis induced by injected neutral sodium phosphate.     

Reduction in Dietary Calcium/Phosphorus Ratio Reduces Bone Mass and Strength in Ovariectomized Rats Enhancing Bone Turnover

To clarify the effects of the dietary calcium (Ca)/phosphorus (P) ratio on bone mineralization under the condition of estrogen deficiency, Wistar strain female rats were ovariectomized (OVX) at 12 weeks old. At 16 weeks old, the rats were divided into three dietary groups fed varying levels of P containing 0.5% Ca: 0.25% P, Ca/P=2; 0.5% P, Ca/P=1; and 1.0% P, Ca/P=0.5 respectively. This study indicates that the reduction of the dietary Ca/P ratio impairs trabecular bone turnover accompanying the acceleration of bone formation in OVX rats.     

Reduction in dietary calcium/phosphorus ratio reduces bone mass and strength in ovariectomized rats enhancing bone turnover

To clarify the effects of the dietary calcium (Ca)/phosphorus (P) ratio on bone mineralization under the condition of estrogen deficiency, Wistar strain female rats were ovariectomized (OVX) at 12 weeks old. At 16 weeks old, the rats were divided into three dietary groups fed varying levels of P containing 0.5% Ca: 0.25% P, Ca/P = 2; 0.5% P, Ca/P = 1; and 1.0% P, Ca/P = 0.5 respectively. This study indicates that the reduction of the dietary Ca/P ratio impairs trabecular bone turnover accompanying the acceleration of bone formation in OVX rats.     

Effect of dietary calcium: Phosphorus ratio on bone mineralization and intestinal calcium absorption in ovariectomized rats

We investigated the effect of dietary calcium:phosphorus (Ca:P) ratio on bone mineralization and intestinal Ca absorption in ovariectomized (OVX) rat models of osteoporosis and sham-operated rats. Thirty 12-wk-old female Wistar rats were divided into three groups of OVX rats and three groups of sham rats. Thirty days after the adaptation period, OVX rats and sham rats were fed a diet formulated Ca:P, 1:0.5, 1:1 or 1:2 (each diet containing 0.5% Ca), respectively for 42 d. In both sham and OVX rats, serum osteocalcin, a marker of bone turnover, was increased by decreasing Ca:P ratio (1:2). In contrast, rats fed the Ca:P = 1:0.5 diet (dietary P restriction) suppressed the increased serum parathyroid hormone, osteocalcin and urinary deoxypyridinoline, and increased Ca absorption in both sham and OVX rats compared to the Ca:P = 1:1 and 1:2 diets. Especially, in OVX rats, the decreased bone mineral density of the fifth lumbar was also suppressed when rats were fed the Ca:P = 1:0.5 diet. These results indicated that the elevation of dietary Ca:P ratio may inhibit bone loss and increase intestinal Ca absorption in OVX rats.     

Decreased mRNA expression of the PTH/PTHrP receptor and type II sodium-dependent phosphate transporter in the kidney of rats fed a high phosphorus diet accompanied with a decrease in serum calcium concentration

This study investigates the phosphorus (P) homeostasis in the process of an altered parathyroid hormone (PTH) action in the kidney of rats fed a high P diet. Four-week-old male Wistar strain rats were fed diets containing five different P levels (0.3, 0.6, 0.9, 1.2 and 1.5%) for 21 days. The serum PTH concentration and urinary excretion of P were elevated with increasing dietary P level. Compared to rats fed the 0.3% P diet, the serum calcium (Ca) concentration remained unchanged, while the serum 1,25(OH)(2)D(3) concentration and urinary excretion of cAMP were elevated with increasing dietary P level in rats fed the high P diets containing 0.6-0.9% P. On the other hand, a lower serum Ca concentration was observed in rats fed the high P diets containing 1.2% or greater P. The serum 1,25(OH)(2)D(3) concentration remained unchanged in rats fed the high P diets containing 1.2% or greater P, comparison with rats fed the 0.3% P diet. The urinary excretion of cAMP and PTH/PTH-related peptide (PTHrP) receptor and type II sodium-dependent phosphate transporter (NaPi-2) mRNA in the kidney were both decreased in rats fed the high P diets containing 1.2% or greater P. In conclusion, a high P diet with subsequent decrease in serum Ca concentration suppressed the PTH action in the kidney due to PTH/PTHrP receptor mRNA down-regulation. Furthermore, an increase in the urinary excretion of P might have been caused by decreased NaPi-2 mRNA expression without the effects of PTH and 1,25(OH)(2)D(3).     

Nutrition and kidney calcification in rats

Nephrocalcinosis is a 'spontaneous' disorder in rats which refers to the deposition of calcium salts in the kidney, preferably in the cortico-medullary region. Studies using defined, semi-purified diets have shown that low dietary concentrations of magnesium, high concentrations of calcium, high concentrations of phosphorus and low calcium: phosphorus ratios induce kidney calcification. Dietary phosphorus induced nephrocalcinosis in female rats is associated with increased kidney size and weight, tubular hyperplasia, fibrosis and increased excretion of albumin in urine. This suggests that nephrocalcinosis may impair kidney function. In rats fed different commercial diets the incidence of nephrocalcinosis can vary considerably. Differences in the degree of nephrocalcinosis in different experiments may negatively influence the comparability of experimental outcome, especially when this is affected by kidney function and structure. Experimental data are needed so that diets can be formulated that do not produce nephrocalcinosis without inducing other disorders.     

Effect of dietary carbohydrates and copper status on blood pressure of rats

Copper deficiency was induced in rats by feeding diets containing either 62% starch, fructose or glucose deficient in copper for 6 weeks. All copper deficient rats, regardless of the dietary carbohydrate, exhibited decreased ceruloplasmin activity and decreased serum copper concentrations. Rats fed the fructose diet exhibited a more severe copper deficiency as compared to rats fed either starch or glucose. The increased severity of the deficiency was characterized by reduced body weight, serum copper concentration and hematocrit. In all rats fed the copper adequate diets, blood pressure was unaffected by the type of dietary carbohydrate. Significantly reduced systolic blood pressure was evident only in rats fed the fructose diet deficient in copper. When comparing the three carbohydrate diets, the physiological and biochemical lesions induced by copper deprivation could be magnified by feeding fructose.     

Gestational and early postnatal dietary NaCl levels affect NaCl intake, but not stimulated water intake, by adult rats

We examined body fluid regulation by weanling (21-25 days) and adult (>60 days) male rats that were offspring of dams fed chow containing either 0.1, 1, or 3% NaCl throughout gestation and lactation. Weanling rats were maintained on the test diets until postnatal day 30 and on standard 1% NaCl chow thereafter. Ad libitum water intake by weanlings was highest in those fed 3% NaCl and lowest in those fed 0.1% NaCl. Adult rats maintained on standard NaCl chow consumed similar amounts of water after overnight water deprivation or intravenous hypertonic NaCl (HS) infusion regardless of early NaCl condition. Moreover, baseline and HS-stimulated plasma Na(+) concentrations also were similar for the three groups. Nonetheless, adult rats in the early 3% NaCl group consumed more of 0.5 M NaCl after 10 days of dietary Na(+) deprivation than did rats in either the 1% or 0.1% NaCl group. Interestingly, whether NaCl was consumed in a concentrated solution in short-term, two-bottle tests after dietary Na(+) deprivation or in chow during ad libitum feeding, adult rats in the 3% NaCl group drank less water for each unit of NaCl consumed, whereas rats in the 0.1% NaCl group drank more water for each unit of NaCl consumed. Thus gestational and early postnatal dietary NaCl levels do not affect stimulated water intake or long-term body fluid regulation. Together with our previous studies, these results suggest that persistent changes in NaCl intake and in water intake associated with NaCl ingestion reflect short-term behavioral effects that may be attributable to differences in NaCl taste processing.     

In-vivo monitoring of corticomedullary nephrocalcinosis in rats using computerized tomography.

An in-vivo method, computerized tomography (CT), was used to monitor nephrocalcinosis in female rats. CT density data correlated well with renal Ca content measured by atomic absorption spectrophotometry. In-vivo CT measurements revealed that the severity of nephrocalcinosis may change spontaneously with time. Manifest calcifications may exhibit spontaneous regression and are probably affected positively by high dietary Mg, in contrast to increased Ca. It is concluded that CT is a suitable and reliable non-invasive in vivo method to follow up time-dependent alterations in kidney calcifications in rats.     

Treatment of the enhanced intestinal uptake of glucose in diabetic rats with a polyunsaturated fatty acid diet

Intestinal absorption of most nutrients is enhanced in diabetic rats. We wished to test the hypothesis that manipulation of dietary fatty acids will modify enhanced uptake of glucose in rats with established streptozotocin-diabetes. Chow-fed control rats or animals with one week of streptozotocin-diabetes were continued on chow or were fed ad libitum for three weeks with semisynthetic isocaloric diets containing a high content of either essential polyunsaturated or non-essential saturated fatty acids. The jejunal and ileal in vitro uptake of varying concentrations of glucose was much higher in diabetic than control rats fed chow or the saturated fatty acid diet. In contrast, the enhanced uptake of this sugar was reduced or normalized in diabetic rats fed the polyunsaturated fatty acid diet. Feeding the polyunsaturated fatty acid diet was associated with increased brush-border membrane activity of alkaline phosphatase in diabetic jejunum and ileum, but neither the saturated fatty acid diet nor the polyunsaturated fatty acid diet altered brush-border membrane cholesterol or phospholipids in control or in diabetic rats. Mucosal surface area was similar in diabetic rats fed the saturated fatty acid diet or the polyunsaturated fatty acid diet. Thus, (1) feeding the polyunsaturated fatty acid diet diminishes the enhanced jejunal and ileal uptake of glucose in diabetic rats, and (2) the influence of the polyunsaturated fatty acid diet on uptake in diabetic rats was not explained by alterations in intestinal morphology or brush-border membrane content of cholesterol or phospholipids. This study suggests that manipulation of dietary lipids may play a role in the normalization of the enhanced intestinal glucose uptake in rats with established diabetes.     

Uptake of radiolabeled copper from portal blood containing fructose or glucose

The present investigation was designed to study the uptake of⁶⁷Cu when administered directly, into the portal vein, along with either functose or glucose, by the liver and extrahepatic tissues. Following weaning, male Sprague-Dawley rats were fed for 3 wk either commercial laboratory ration (chow) or semipurified diets deficient in Cu (0.6 ppm) or supplemented with Cu (6.0 ppm) and containing 62% carbohydrate as either fructuse or cornstarch. After an overnight fast, a single dose of rat plasma (0.1 mL) containing fructose or glucose extrinsically labeled with⁶⁷Cu was injected directly into their portal vein. Although not always statistically significant, rats fed chow retained more radioactivity in the liver and several extrahepatic tissues when⁶⁷Cu was administered with fructose than with glucose. Regardless of Cu status, rats fed diets containing fructose retained more radioactivity in extrahepatic tissues than rats fed starch. There was an increased uptake of⁶⁷Cu by the liver, blood, muscle, and fat pad when fructose as compared to glucose was injected in combination with the isotope. These data strongly suggest that Cu requirements or utilization are greater when fructose is the main dietary carbohydrate. The results may also in part explain the reason for the increased severity of Cu deficiency in rats fed fructose.     

Partial replacement of monocalcium phosphate with neutral phytase in diets for grass carp,Ctenopharyngodon idellus

A 9‐week experiment was designed to study the effects of partial replacement of monocalcium phosphate (MCP) with neutral phytase on growth, body compositions, serum biochemical statuses and intestinal digestive enzyme activities of grass carp, Ctenopharyngodon idellus. The control diet (designated as P2.0) was prepared with 2.0% MCP but without phytase. The three other diets (designated as PP1.5, PP1.0 and PP0.5, respectively) were supplemented with 1.5, 1.0 and 0.5% MCP, respectively, along with 500 FTU of neutral phytase kg^?1 diet in each. After a 9‐week feeding trial, fish (initial body weight: 43.44 ± 2.37 g) fed with PP1.5 and PP1.0 had no significant change in weight gain (WG), specific growth rate (SGR), protein efficiency rate (PER) or feed conversion ratio (FCR) compared with the control (P > 0.05) whereas fish fed with PP0.5 showed significantly lower growth performance in the above parameters. The crude lipid content in whole body or muscle of the fish fed with PP1.5 was significantly lower than the control while significantly higher in fish fed with PP0.5 (P < 0.05), whereas no obvious change was observed in the fish fed with PP1.0. For serum indices, higher serum alkaline phosphatase (Alkp), phosphorus (P) and calcium (Ca) contents were observed in fish fed with phytase‐supplemented diets in comparison with the control. In addition, dietary phytase supplementation increased amylase activity and decreased lipase activity in both foregut and hindgut. The present study suggests that dietary MCP can be reduced when neutral phytase is added to the grass carp diet, and that the maximum MCP reduction level can be up to 1% when neutral phytase is supplemented at 500 FTU kg^?1 diet.     

Proinflammatory gene expression and renal lipogenesis are modulated by dietary protein content in obese Zucker fa/fa rats

Obesity is a risk factor for the development of chronic kidney disease (CKD) and end-stage renal disease. It is not clear whether the adoption of a high-protein diet in obese patients affects renal lipid metabolism or kidney function. Thus the aims of this study were to assess in obese Zuckerfa/fa rats the effects of different types and amounts of dietary protein on the expression of lipogenic and inflammatory genes, as well as renal lipid concentration and biochemical parameters of kidney function. Rats were fed different concentrations of soy protein or casein (20, 30, 45%) for 2 mo. Independent of the type of protein ingested, higher dietary protein intake led to higher serum triglycerides (TG) than rats fed adequate concentrations of protein. Additionally, the soy protein diet significantly increased serum TG compared with the casein diet. However, rats fed soy protein had significantly decreased serum cholesterol concentrations compared with those fed a casein diet. No significant differences in renal TG and cholesterol concentrations were observed between rats fed with either protein diets. Renal expression of sterol-regulatory element binding protein 2 (SREBP-2) and its target gene HMG-CoA reductase was significantly increased as the concentration of dietary protein increased. The highest protein diets were associated with greater expression of proinflammatory cytokines in the kidney, independent of the type of dietary protein. These results indicate that high soy or casein protein diets upregulate the expression of lipogenic and proinflammatory genes in the kidney.     

Dietary P regulates phosphate transporter expression,phosphatase activity,and effluent P partitioning in trout culture

Phosphate utilization by fish is an important issue because of its critical roles in fish growth and aquatic environmental pollution. High dietary phosphorus (P) levels typically decrease the efficiency of P utilization, thereby increasing the amount of P excreted as metabolic waste in effluents emanating from rainbow trout aquaculture. In mammals, vitamin D₃ is a known regulator of P utilization but in fish, its regulatory role is unclear. Moreover, the effects of dietary P and vitamin D₃ on expression of enzymatic and transport systems potentially involved in phosphate utilization are little known. We therefore monitored production of effluent P, levels of plasma vitamin D₃ metabolites, as well as expression of phosphatases and the sodium phosphate cotransporter (NaPi2) in trout fed semipu diets that varied in dietary P and vitamin D₃ levels. Mean soluble P concentrations varied markedly with dietary P but not with vitamin D₃, and constituted 40–70% of total effluent P production by trout. Particulate P concentrations accounted for 25–50% of effluent P production, but did not vary with dietary P or vitamin D₃. P in settleable wastes accounted for <10% of effluent P. The stronger effect of dietary P on effluent P levels is paralleled by its striking effects on phosphatases and NaPi2. The mRNA abundance of the intestinal and renal sodium phosphate transporters increased in fish fed low dietary P; vitamin D₃ had no effect. Low-P diets reduced plasma phosphate concentrations. Intracellular phytase activity increased but brushborder alkaline phosphatase activity decreased in the intestine, pyloric caeca, and gills of trout fed diets containing low dietary P. Vitamin D₃ had no effect on enzyme activities. Moreover, plasma concentrations of 25-hydroxyvitamin D₃ and of 1,25-dihydroxyvitamin D₃ were unaffected by dietary P and vitamin D₃ levels. The major regulator of P metabolism, and ultimately of levels of P in the effluent from trout culture, is dietary P.Communicated by: C.-H. Wang     

Absence of effect of the incorporation of a milk phosphopeptide on the utilization of calcium and phosphorus in the young pig

Casein phosphopeptides are known to influence calcium absorption. A 50-day study was performed in 6-week old pigs fed either a control diet or a 5% casein phosphopeptide-containing diet (PP group). Both diets provided similar amounts of Ca (0.8%), P (0.5%), proteins, energy and vitamins. PP diet provided near 1/2 of total Ca, 1/3 of total P and 1/5 of proteins in the form of casein phosphopeptide. Ca and P excretion, absorption and retention were evaluated during a 10-day balance study. Bones were collected at slaughter to determine density, bending moment and bone mineral content. Calcium absorption and bone parameters (urinary hydroxyproline included) were not influenced by the type of diet. P absorption, but not retention, was slightly higher in the control group. Urinary Ca was higher and urinary P lower in PP pigs than in controls. These changes might result from the different kinds of dietary phosphorus, inorganic versus phosphopeptide, rather than from the difference between dietary proteins.